在 C++ 中，如何测试与“|"结合的几个标志之一?在一个论点? [英] In C++, how can I test for one of several flags combined with "|" in one argument?

问题描述

我有下一个代码:

int main()
{
 OwnSelect(23, FD_READ | FD_WRITE); // <---- Several arguments as one
 return 0;
}

int OwnSelect(SOCKET s, long lNetworkEvents)
{
 // How can i check that FD_READ has been passed?
 if(lNetworkEvents == FD_READ)
 {
  // never here
 }
 return 0;
}

无论是否已通过 FD_READ 传递了另一个 FD，我如何检查是否已传递 FD_READ.谢谢！

How can i check that FD_READ has been passed no matter if another FD has been passed with FD_READ. Thanks!

推荐答案

似乎您在这里错过了一些基本的位操作.您正在对 FD_READ 和 FD_WRITE (| = 按位或) 进行 OR 运算，从而将这两个值指示的位设置为参数.要检查 FD_READ 是否通过，您需要将 lNetworkEvents 与 FD_READ 进行 AND 运算并检查结果是否等于 FD_READ，如下所示:

Seems like you're missing out on a bit of basic bit manipulation here. You're OR'ing FD_READ and FD_WRITE (| = bitwise OR), thereby setting the bits indicated by both values, as a parameter. To check if FD_READ was passed, you need to AND lNetworkEvents with FD_READ and check if the result equals FD_READ, like so:

<代码>if (FD_READ == (lNetworkEvents & FD_READ)) { ... }

这当然假设 FD_READ 和 FD_WRITE 是旨在以这种方式使用的值(即通常没有重叠位).

This of course assuming that FD_READ and FD_WRITE are values that were meant to be used this way (i.e. typically don't have overlapping bits).

已修复，wabepper 绝对正确:) 哎呀！

edit: fixed, wabepper is absolutely right :) oops!

这篇关于在 C++ 中，如何测试与“|"结合的几个标志之一?在一个论点?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！